When to Apply Potassium Bicarbonate to Grapes?

Powdery mildew loves to feed on grapes.

Growing grapes (Vitis) requires a combination of exceptional patience, hard work and vigilance. Grown in U.S. Department of Agriculture plant hardiness zones 2 through 10, grapes are susceptible to a range of diseases, including powdery mildew. This disease, caused by the fungal species Uncinula necator, attacks only the surface of grapes, creating a dusty grayish-white substance which continues to spread unless interrupted by water or certain fungicides, such as potassium bicarbonate.

Timing is Everything

Start applying potassium bicarbonate within seven days of the first sign of powdery mildew, followed by repeat applications every seven to 14 days thereafter to control and protect against further development of the disease. Follow the directions of the specific fungicide regarding when to stop using the treatment before harvest.

Concerted Efforts

Controlling powdery mildew and other grape diseases requires a combination of cultural and chemical tactics. Prune overcrowded vines to increase air circulation, reduce relative humidity around the vines by watering from below rather than using overhead spraying and remove infected leaves, branches and fruits to further decrease spread. When employing chemical prevention methods, The Ohio Agricultural Research and Development Center recommends using a combination of fungicides during the growth cycle to prevent the development of resistant strains of powdery mildew.

About the Author

Based in Ohio, Deborah Waltenburg has been writing online since 2004, focusing on personal finance, personal and commercial insurance, travel and tourism, home improvement and gardening. Her work has appeared on numerous blogs, industry websites and media websites, including "USA Today."